EUP3484S
loop has the unity gain is important. Lower crossover
frequencies result in slower line and load transient
responses, while higher crossover frequencies could
cause the system instability. A good standard is to set
the crossover frequency below one-tenth of the
switching frequency.
If this is the case, then add the second compensation
capacitor (C4) to set the pole fP3 at the location of the
ESR zero. Determine C4 by the equation:
C2 R
ESR
C4 =
R3
To optimize the compensation components, the
following procedure can be used:
To simplify design efforts using the EUP3484S，the
typical design for common application are listed in
Table1.
1. Choose the compensation resistor (R3) to set the
desired crossover frequency.
External Bootstrap Diode
Determine R3 by the following equation:
It is recommended that an external bootstrap diode be
added when the system has a 5V fixed input or the
power supply generates a 5V output. This helps
improve the efficiency of the regulator.
2π C2 f
V
C
OUT
R3 =
G
G
V
FB
V
EA
CS
2π C2 0.1 f
S
OUT
<
G
G
V
FB
EA
CS
Where fC is the desired crossover frequency, which is
typically below one tenth of the switching frequency.
2. Choose the compensation capacitor (C3) to achieve
the desired phase margin. For applications with
typical inductor values, setting the compensation
zero (fZ1) below one-forth of the crossover
frequency provides sufficient phase margin.
Figure 3. Add Optional External Bootstrap Diode
to Enhance
Determine C3 by the following equation:
This diode is also recommended for high duty cycle
4
C3 >
V
2π R3 f
OUT
operation ( when
>65% ) and high output
C
V
IN
Where R3 is the compensation resistor.
voltage (VOUT >12V) applications.
3. Determine if the second compensation capacitor
(C4) is required. It is required if the ESR zero of
the output capacitor is located at less than half of
the switching frequency, or the following
relationship is valid:
f
1
S
2
<
2π C2 R
ESR
Table1. External Components for Typical Designs
Vin(V)
Vout(V)
1.0
L1(µH)
3.3
C2(µF)
22*2
22*2
22*2
22*2
22*2
22*2
22*2
R1(Kꢀ)
0.820
3.0
R2(Kꢀ)
10
R3(Kꢀ)
6.8
C3(nF)
3.9
C4(pF)
open
open
open
open
open
open
open
5
5
1.2
4.7
10
6.8
3.9
5
3.3
10
26.1
10
6.8
3.9
12
12
12
12
1.0
3.3
0.820
3.0
10
2.2
10
1.2
4.7
10
2.2
10
3.3
10
26.1
10
6.8
3.9
5.0
10
44.2
10
6.8
3.9
DS3484S Ver1.2 May 2012
10
EUTECH [ EUTECH MICROELECTRONICS INC ]
